The present invention relates to a lithium ion type nonaqueous electrolyte-secondary battery which is improved in the discharge quality and the cycle properties or the charge-discharge cycle life.
There have actively been investigated nonaqueous electrolyte-secondary batteries which make use of, as negative electrode-active materials, lithium-containing light metal alloys or substances capable of absorbing and releasing lithium ions because of their high electic voltages and high energy densities. On the other hand, there have generally been use d lamellar compounds which make use of intercalation of Li such as LiMn.sub.2 O.sub.4, Li.sub.2 MnO.sub.3, LiCoO.sub.2, LiCo.sub.0.5 Ni.sub.0.5 O.sub.2, LiNiO.sub.2 and MoS.sub.2 as positive electrode-active materials for secondary batteries. In particular, LiCoO.sub.2 as disclosed in Japanese Un-examined Patent Publication (hereunder referred to as "J.P. KOKAI") No. Sho 55-136131 is useful because it can provide a battery having a high discharge voltage of not less than 3.5 V and a high capacity. However, the crystalline structure thereof gradually destroyed as the battery is repeatedly charged and discharged, the destruction of the crystalline structure becomes conspicuous if the degree of discharge is increased for the absorption of Li and the deterioration of the quality thereof proceeds. In respect of the charge-discharge cycle properties, however, it requires an improvement in stability of voltage and capacity like most of other materials for positive electrodes. Under such circumstances, there have been proposed in, for instance, Japanese Unexamined Patent Publication (hereunder referred to as "J.P. KOKAI") Nos. Hei 4-61760, Hei 4-162357, Hei 3-201368 and Hei 4-267053, methods for improving the charge-discharge characteristics and cycle properties of these secondary batteries which utilize compound oxides obtained by further adding polyvalent transition metals to the foregoing active materials. These methods permit improvement in the cycle properties such as stabilization of voltages, but they cannot simultaneously improve battery qualities such as capacity and discharge voltage. Moreover, the use of many polyvalent metals, in place of metals such as Co, Mn and Ni, has variously been proposed, but there has not yet been investigated any effect accomplished by the simultaneous use of polyvalent metals and monovalent alkali metals usable in place of Li.